JPS58224559A - Switching circuit - Google Patents

Abstract

PURPOSE:To enable to stably operate a switching circuit even when a load varies by connecting a series circuit of a capacitor and an inductance in parallel with a switching element and obtaining an output from both terminals of the inductance. CONSTITUTION:An input DC voltage 1 is switched by a switching transistor 3 which is connected in parallel with the first capacitor 5 through the first inductance element 2. A series circuit of the second capacitor 7 and the second inductance element 8 is connected in parallel with the transistor 3, and a voltage which is presented across the second inductance element 8 is produced as an output.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a switching circuit 1'' used in switching power supplies, power amplifiers, and the like.

[Technical background of the invention and its problems]

In recent years, with the development of microcomputers and other devices, switching power supplies, which are small, lightweight, and highly efficient, have been widely used in everything from industrial equipment to household electrical appliances. In the field of amplifiers, switching amplifiers such as class D amplifiers and class E amplifiers are used.Therefore, various types of switching circuits have been devised for these switching power supplies and amplifiers. .

As an example of a switching circuit used in conventional switching power supplies, the input DC voltage is switched by a switching element via the primary winding of a transformer, and the AC generated in the secondary winding of the transformer is rectified, smoothed, and output. There is a circuit that does this.

However, in such a circuit, the input DC voltage is switched in a square waveform, so the harmonic components generate a lot of noise, which has a negative impact on the load and surrounding equipment. Because the voltage and current changes are steep during on and turn-off, the voltage and current waveforms overlap during these transitions, causing so-called switching loss.As the switching frequency increases, this loss becomes so large that it cannot be ignored. Become.

This leads to deterioration of power transmission efficiency and generation of large amounts of heat.

These drawbacks are common to most switching circuits that perform rectangular five-switching of the input DC voltage.

To solve this problem, a resonant switching circuit has been devised.

This is a circuit in which an LC resonant circuit is inserted into the circuit, and the voltage or current waveform at the switching element is converted into a resonant waveform.
In the circuit. Since the voltage and gate current shapes are resonant waveforms, there is little harmonic noise, and the switching elements turn on and turn! Since the voltage and current change slowly when off, the circuit has extremely low switching loss.

In these circuits, the voltage waveform of the switching element becomes a resonant waveform, and the circuit whose current waveform becomes a resonant waveform is called a voltage resonant switching circuit.

As an example of such a resonant switching circuit,
6 Nikkei Electronics” 1976°3.22181
The class E amplifier described on pages 27 to 141 is well known.

However, in the resonant switching circuit shown in this document, since the LC resonant circuit and the load are connected in series, the resonant switching circuit operates under a certain load (2) with extremely low noise and switching loss; If the value fluctuates, the resonance condition will be deviated from, and in the worst case, the resonant capacitor or inductance element (= stored energy will be short-circuited by the switching element). Ta.

[Purpose of the invention]

An object of the present invention is to provide a resonant switching circuit that operates stably without deviating from the resonant condition even when the load changes.

[Summary of the invention]

This invention applies input DC voltage to a switching element connected in parallel with a first capacitor via a first inductance element, and connects the series circuit of the second capacitor and the second inductance element to the switching element connected in parallel with the first capacitor through the first inductance element. A resonant switching circuit connected in parallel with a switching element (
Second, the present invention is characterized in that the voltage appearing across the second inductance element is taken out as an output.

〔Effect of the invention〕

According to this invention, the voltage and current waveforms in the switching element and the circuit are resonant waveforms, and harmonic noise is extremely small compared to the case where switching is performed in a square waveform.

In addition, when the switching element turns on, the voltage across it is already zero, so there is no switching loss at all when the switching element turns on.On the other hand, when it turns off, the current is smaller than the peak power supply when it is on.・Since it can be turned off and the voltage rises slowly, there is little switching loss at turn-off.

Therefore, switching loss is extremely low compared to conventional circuits.

In particular, by connecting the two loads in parallel with the inductance element of gIj42, the switching circuit itself forms a closed circuit and is less affected by the load, so the resonance conditions are disturbed even for load fluctuations. Therefore, the original operation of the resonant switching circuit can be maintained stably.

[Embodiments of the invention]

FIG. 1 shows an embodiment of the present invention. In the figure, reference numeral 1 denotes an input DC power source, the positive end of which is connected via a first inductance element 2 to the collector of a switching element (for example, an NPN) transistor 3. A drive circuit 4 is connected to the base of the transistor 3 to open and close the transistor 3 at a predetermined period and with a predetermined conduction width. The emitter of the transistor 3 is connected to the negative terminal of the power supply 1 (
A first capacitor 5 and a damper diode 6 are connected in parallel between the collector and emitter of the transistor 3. Furthermore, a series circuit of a capacitor 7 and a second inductance element 8 is connected in parallel between the collector and emitter of the transistor 3.

Both ends of the second inductance element 8 are connected to output terminals 11 and 12, from which power is supplied to a load (not shown).

In the above configuration C=, the voltage and current waveforms at the collector of the transistor 3 are operated in a resonant waveform, and in particular, the voltage increases once and then decreases to 0 (V) again. , the switching period and conduction width of transistor 3.

1st. The inductance value of the second inductance element 2.8, the capacitance value of the first and l'G2 capacitors 5.7, etc. are mutually set in advance. Among these, the first inductance element 2 mainly operates as a constant current source, although it also affects the resonance conditions. Also, to simplify the explanation, transistor 3 and diode 6 are assumed to be ideal switches.

It is assumed that the circuit is operating in a steady state.

The operation of the switching circuit configured in this manner (-) is
Explain using the factors. Figure 2 (al is the collector current IO of transistor 3, (b) is the collector-emitter voltage Vo11 of transistor 3. (cl is the current I OO of transistor 3, (d) 3 is a waveform diagram of a line output voltage vO. FIG.

First, at t, the transistor 3 begins to conduct. At the time (2), the current of the inductance element 2 and the ML flow I00 of the capacitor 7 have the same value.

Period 1o- during which transistor 3 is 1 conduction "1"-
1, the collector current Io draws an arc of resonance and gradually becomes (
Two rises, reaches the peak, and then falls. The resonant frequency of this arc is influenced by the value of the inductance element 2, but is mainly determined by the value 1 of the capacitor 7 and the inductance element 8.

Next 1 = Transistor 3 is cut off at time tl: 6 is non-conducting ``C2'' When the capacitor 5 starts to be charged by the energy 1 U stored in the inductance element 2.8, its voltage reaches its peak value. When the voltage reaches 0 (V), it starts discharging, and at point 1, it becomes 0 (Vl) and tries to be charged to a negative voltage, but since the diode 6 is forward biased and becomes conductive, the voltage of the capacitor 5 becomes 0 (v)l2. In this way, for one period $, ~t, l2, the voltage of the capacitor 5, that is, the collector voltage of the transistor 3 increases.
The emitter voltage VOR gradually changes in a sinusoidal arc. The resonant frequency of this voltage Vog is determined by the inductance value of the inductance element 2゜8 and the capacitor 5,
The capacitance value of 7 is determined by mutual understanding.

Next, after the diode 6C'-current begins to flow.

During the period from 1 to t until the current reaches 0 (AI),
The collector-emitter voltage Vag of transistor 3 is O
(The current value of the inductance element 2 and the current value of the capacitor 7 become i2), and at the time t3, the transistor 3 starts conducting again.

The operation during the above periods t and t is the operation within one period of the switching circuit of FIG. 1, and such operation is periodically repeated. At this time, as shown in Figure 2 (C
) As shown in (d) (the voltage and current waveforms in the two circuits become resonant waveforms close to sine waves.

In addition, the peak value of each waveform diagram in FIG. 2 (=1 to (d)), the power value supplied to the load, etc. are the voltage value of the power source 1, the impedance value of the load, the inductance value of the inductance element 3°8, This is determined by the capacitance values of the capacitors 5 and 7, etc.

As is clear from the above explanation, in this switching circuit, the voltage at each part and the i4 current waveform are resonant waveforms, so
Extremely low harmonic noise. Furthermore, even if the current flowing through the transistor 34 decreases after a certain transient period when the transistor 3 is cut off or turned off at time t, the current value at the moment when the transistor 34 turns off is smaller than the peak current. , transistor 3
(The voltage across the circuit slowly rises.) Second, the switching loss at turn-off is lower than in conventional switching circuits. And t. When the transistor 3 conducts, that is, turns off at time points t and t, the voltage across it is already f0, so there is no switching loss at the time of turn-on. For these reasons, even if the switching frequency becomes high, the switching loss is negligibly small compared to conventional switching circuits, so the power transfer efficiency is high.

Fever is also reduced.

Further, since the load is connected in parallel with the second inductance element 8 and the switching circuit itself is a closed circuit, it is affected by the load. In other words, for load fluctuations below the maximum output voltage obtained by the set constant value of the circuit, the switching period of switching 3,
By slightly adjusting the conduction width, the resonance condition will not be exceeded, and sufficiently stable operation can be obtained.

In the above embodiment (=), the input signal (
= If appropriate modulation (pulse width modulation) is applied, it can also be used as a highly efficient switching type power amplifier.

Other embodiments of the present invention are shown in FIGS. 3 to 5. FIG. 3 shows an example in which the second inductance element 8 in FIG. 1 is replaced with the primary windings 9 & 11 of the transformer 9, and both ends of the secondary winding 9b of the transformer 9 are connected to the output terminals. In this case, strictly speaking, the excitation inductance of the transformer 9 is as shown in Figure 1 (
It has the same function as the second inductance 8 in the second inductance.

By using the transformer 9 in this manner, the switching circuit and the load can be isolated, and the output voltage can be set arbitrarily by the winding ratio C2.

Figure 4 shows the 1'th winding 9 &
This is an example in which a second inductance element 8 is connected in parallel with I. In this case, as long as the excitation inductance value of the transformer 9 is larger than the resonance 1'-required inductance value, the resonance frequency etc. can be adjusted by the inductance element 8, which has the advantage that the design of the transformer 9 is relatively easy. There is. Incidentally, the inductance element 8 is the 2nd part of the transformer 9.
It may be connected in parallel to the next winding.

FIG. 5 shows an example in which the present invention is applied to a switching type power converter, in which the secondary winding 9bl of the transformer 9 shown in FIG. 3 is connected to the two rectifying and smoothing circuits 10. This rectifying and smoothing circuit 10
Output (DC power is obtained from the dll to the output terminals 11 and 12. In this case.

Of course, if there is no need for insulation or voltage conversion, the transformer 9 may be replaced with the inductance element 8.

Although several embodiments have been described above, it is also possible to configure these embodiments by appropriately combining them. In addition, in the above explanation, all the switching elements 3 have been described as NPN transistors, but any element capable of switching may be used. Furthermore, by setting the resonance conditions, it is possible to operate in such a way that no current flows through the Dannoher diode 6, so in that case, the damper diode 6 is not necessary. Also, the damper diode 6 is connected to the transistor 3
It may be connected between the base and emitter of.

[Brief explanation of the drawing]

FIG. 1 is a circuit configuration diagram showing one embodiment of the invention, FIG. 2 is an operation waveform diagram of each part thereof, and FIGS. 3 to 5 are circuit configuration diagrams showing other embodiments of the invention. DESCRIPTION OF SYMBOLS 1... Input DC power supply, 2... First inductance element, 3... Switching element, 4 drive circuit i,
i... First capacitor, 6... Damper-9 diode, 7... Second capacitor f, 8... Second inductance element, 9... Transformer, 10! ... Rectifier and smoothing circuit, 11.12... Output terminal. Applicant's Representative Patent Attorney Takehiko Suzue Figure 3 Figure 4 Figure 5

Claims (3)

[Claims] (1) A switching element connected to an input DC power source via a first inductance element and controlled to open and close at a predetermined period and a predetermined conduction width; a first capacitor connected in parallel with the switching element; A switching circuit comprising a series circuit of a second capacitor and a second inductance element connected in parallel with the element, and a voltage across the second inductance element is taken out as an output. (2) The switching circuit according to claim 1, characterized in that the primary winding of a transformer is used as the second inductance element, and the output is taken out from the secondary winding of this transformer. (3) The switching circuit according to claim 1, wherein the voltage appearing between both ends 1' of the second inductance element is taken out as an output via a transformer.